C1738

CIRCUIT DESCRIPTION
The Electronic Leveling Control (ELC) exhaust solenoid valve is controlled (switched ON/OFF) by the Continuously Variable Road Sensing Suspension (CVRSS) control module. The control module provides a low-side drive (switched to ground) whenever exhaust activity is required and during a "head-relief" sequence which occurs before each compressor start-up. This drive output from the CVRSS control module is continually monitored to determine if the voltage level agrees with the commanded state.

CONDITION FOR SETTING THE CODE "CURRENT"
The CVRSS control module measures a feedback voltage at pin "C 14" less than a preset threshold during an exhaust solenoid valve OFF-state.

ACTIONS TAKEN WHEN CODE SETS
^ ALL rear leveling activity for the remainder of the ignition cycle will be disabled.
^ The "SERVICE RIDE CONTROL" message will be displayed.

CONDITION FOR CODE TURNING "HISTORY"
The CVRSS control module no longer senses a low voltage at pin "C14" when the exhaust solenoid valve is in an OFF-state.

HOW TO CLEAR THE CODE
^ Use the scan tool.
^ Use the On-Board diagnostic "CLEAR RSS CODES" feature.

TEST DESCRIPTION
The numbers below refer to step numbers on the diagnostic table.
2. Checks to see if the "Electronic Suspension Control" circuit breaker is tripped.
3. Checks for an open in circuit 1340.
4. Checks for an internal open in the exhaust solenoid valve.
5. Checks for a short to ground in circuit 320.
6. Checks for an open in circuit 320.
7. Checks for an internal short in the exhaust solenoid valve.
8. Checks for short to ground in circuits 1340 and 322.
9. Checks for a short to ground in the compressor assembly pigtail or internally to the compressor assembly.

DIAGNOSTIC AIDS
A temporary compressor overload (i.e. high head pressure during a cold start) may cause the "Electronic Suspension Control" Maxi circuit breaker to trip. This is one possible cause of C1738.

A Code C1738 fault condition is detectable only when the exhaust solenoid valve output is commanded to the OFF-state, which occurs whenever exhaust activity is not required. The CVRSS control module expects to see a high voltage during the OFF-state.

Only electrical problems with the exhaust solenoid valve are nagged. Pneumatic blockage problems do not set a code, but the CVRSS control module shuts off the exhaust function if no progress is made, or if excessive run time occurs. Recovery is not attempted until ignition is cycled OFF and ON.

Important: Check for disconnected or damaged air lines and replace if found.